This invention relates to die cutting apparatus. More specifically, this invention relates to apparatus for locking a die sheet to be in surface-to-surface contact with a die roller to provide true cylindrical presentation of the die sheet.
This invention also incorporates a novel bridge means for providing a continuous die cutting surface even in the area of the die sheet locking means.
Equipment for cutting and scoring continuous webs of material such as paper, sheet metal, cardboard and the like is relatively high speed, sensitive equipment. Broadly speaking such equipment falls into two general categories, reciprocating equipment and rolling equipment. Reciprocating equipment utilizes an upper die and a lower die of flat construction which are brough together by apparatus such as stamping presses or the like to make an impression on the material being formed. Where the material being formed is a continuous web there also are required equipment such as accumulators so as to permit continuous operation of other portions of the line, e.g. printing stations and the like, without causing interruption in the production line velocity. Rolling equipment utilizes a pair of cylindrical die rollers. The material being worked is passed therebetween and the cooperating rollers cut or score the material.
Those having skill in these arts will recognize that utilization of reciprocating equipment presents serious disadvantages. Interrupted advancement of the workpiece web causes tensile stresses which sometimes cause tearing or rupture of the material. Additionally, continued web advancement in other areas of the production line require the use of accumulators in conjunction with the die cutting apparatus. Further, use of reciprocating equipment with respect to work requiring continuing die cut registry presents difficult alignment problems.
Rotary die cutting equipment, of course, is much better able to handle die cutting for continuously advancing work products. Where, however the cut repeat is not consistent with the circumference of the die roller, problems have arisen both with respect to registry and with respect to the bridge between the die surfaces in the area of the die securing structure. More specifically, known methods of securing die sheets to die rollers have included structure which result in a gap between the transverse edges of the die sheet. Where attempts have been made to close the gap between the transverse edges of the die sheet, it has been found to be difficult to effect continuing registry of the die sheet on consecutive rotations.
A still further problem presented by rotary die structure such as those presently known is the difficulty attendant to obtaining a solid surface-to-surface contact between the die sheet and the die roller. Failure to obtain this surface-to-surface contact results in a non-cylindrical surface presentation and a non-solid backing for the die thereby diminishing the cutting efficiency of the die surface.
Although those dealing in these arts have addressed themselves to these problems for a number of years, no satisfactory solutions have been proposed.